1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus. More specifically the present invention relates to an optical recording/reproducing apparatus having a 3T-component compensating circuit, in which among the level-shifted radio frequency signals shifted during a reproduction of the recorded data from an optical disc, the level-shift of the 3T component is compensated for, so that error corrections may be carried out by a digital signal processor.
2. Description of the Related Art
Generally, the optical disc which is used in a CDP (compact disc player), LDP (laser disc player) or DVD (digital versatile disc) is not damaged by external factors such as temperature, humidity and the like. Further, the data which is recorded on the optical disc can be reproduced clearly by laser beams, and therefore, its use has widely propagated.
In the optical recording/reproducing apparatus, the video and audio data recorded on the disc are reproduced by a pickup by using laser beams, and the reproduced data is outputted through a monitor and a speaker.
Under this condition, the radio frequency signals (RF signals) which are reproduced by the pickup include a frequency component corresponding to the pitches of 3T-11T of the optical disc. The digital signal processing section carries out error corrections by utilizing the frequency component corresponding to the 3T pitch (to be called a "3T component" below) which contains the largest amount of data.
In order to carry out the error corrections by utilizing the 3T component by the optical pickup, the 3T component has to be amplified, and the circuit for this amplification is a peaking circuit.
If accurate error corrections are to be carried out, the duty cycle of the output wave of the peaking circuit has to be maintained at 50%.
In an earlier arrangement, a peaking circuit containing an operational amplifier has been used. The peaking circuit amplifies the sinusoidal waves input thereto but unfortunately the resultant output is level-shifted so as to no longer have a 50% duty cycle.
Accordingly, a digital signal processor can not properly error correct the signal output from the peaking circuit.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited optical recording/reproducing apparatus having a 3T component compensating circuit in accordance with the present invention: U.S. Pat. No. 5,719,847 to Tateishi et al., entitled Optical Disk Player Having Wave form Distortion Compensating Function, U.S. Pat. No. 5,623,466 to Itonaga, entitled Optical Pickup Apparatus With Skew Error Control And Optical Information Recording And/Or Reproducing Apparatus Using The Same, U.S. Pat. No. 5,500,842 to Dunlavy, entitled Method And Apparatus For Correcting Distortion In Compact Disc Recording And Playback System, U.S. Pat. No. 5,502,698 to Mochizuki, entitled Automatic Attitude Correcting System For Optical Disc Device, U.S. Pat. No. 5,550,797 to Kimura et al, entitled Optical Reproduction Signal Processing Circuit For Producing An RF Signal And A Servo Signal With A High Signal To Noise Ratio Even Though The RF Signal Component And The Servo Signal Component Partially Overlap In Frequency Distribution, U.S. Pat. No. 5,253,240 to Yanagawa, entitled Tracking Error Detecting System For Removing An Offset In An Optical Disk Player, U.S. Pat. No. 5,737,371 to Jaquette, entitled Realignment Of Data Stream From An Optical Disk, U.S. Pat. No. 5,706,267 to Kimura et al, entitled Method And Apparatus For Retrieving Data From A Storage Device, U.S. Pat. No. 5,710,750 to Tachibana, entitled Optical Disc Device, U.S. Pat. No. 5,726,963 to Ohta, entitled Information Reproduction Apparatus Including A Phase Compensation Circuit For Eliminating The Influence Of AC-Coupling, U.S. Pat. No. 5,659,535 to Kimura et al., entitled Method For Retrieving Data From A Storage Device, and U.S. Pat. No. 5,675,569 to Yamaguchi et al., entitled Readback Circuit For An Optical Information Reading And Recording Apparatus.